Is it possible to subirrigate bonsai trees? Has anyone had any luck with that? And if normal bonsai potting mixture doesn't suck up water that well, is it possible to add a little clay or something to the mixture to make it suck up enough water to keep the mixture moist enough without for that matter making it bad in some way for the tree? I have two bonsai trees --- an oak and a juniper --- and I would really like to subirrigate them if that is possible.